To meet a requirement for a voice service in a network that does not support a voice over Long Term Evolution (LTE) (Voice over LTE, VoLTE) function, a circuit switched fallback (CSFB) technology is used in the existing 3GPP. The CSFB enables user equipment (UE) to fall back to a Global System for Mobile Communications (GSM) network or Universal Mobile Telecommunications System (UMTS) network. If CSFB user equipment falls back to the UMTS network, in a process in which a circuit switched (CS) service is performed, a packet switched (PS) service may be concurrently performed, and the PS service may not end when the CS service ends. In the prior art, a method shown in FIG. 1 is used to implement fast return of the CSFB user equipment.
Step 1: The UE sends a disconnect (disconnect) message to a mobile switching center (MSC).
Step 2: The MSC sends a release (release) message to the UE.
Step 3: The UE sends a release complete (release complete) message to the MSC.
Step 4: The MSC sends an Iu release command (Iu release command) to a radio network controller (RNC).
Step 5: The RNC sends a radio link reconfiguration prepare (radio link reconfiguration prepare) message to a base station.
Step 6: The base station sends a radio link reconfiguration ready (radio link reconfiguration ready) message to the RNC.
Step 7: The RNC sends a radio bearer release (radio bearer release) message to the UE.
Step 8: The base station sends a radio link reconfiguration commit (radio link reconfiguration commit) message to the RNC.
Step 9: The UE sends a radio bearer release complete (radio bearer release complete) message to the RNC.
Step 10: The RNC sends an Iu release complete message to the MSC.
Step 11: Initiate PS release when a PS inactivity timer expires, where duration of the inactivity timer may be used to limit time during which the UE is in a PS inactive state.
Step 12: The RNC sends a radio resource control (RRC) connection release (RRC connection release) message, where the RRC connection release message carries target frequency information.
Step 13: The UE fast returns to an LTE network according to the target frequency information.
Step 14: Release PS service resources of an Iu interface and an Iub interface.
It can be seen from FIG. 1 that before returning to the LTE network, the UE needs to complete CS service release, PS service release, and RRC connection release processes. An entire release process is complex and takes a long time. Therefore, a delay for the CSFB user equipment to return to the LTE network is extremely long, and consequently, user experience becomes poor.